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Astronomy is perhaps the oldest science. The ancients saw cosmic
meanings in the stars, and they organized their lives around
lunar and solar cycles (i.e. the month and year). They also
observed the solstices, the equinoxes, and of course the four
seasons. Over many centuries the "precession of the equinoxes"
corrupted Julius Caesar's ancient calendar (the Julian
calendar); in 1586 it was replaced with the Gregorian calendar,
which features the system of leap years we know today.
Aristotle's
earth-centered ("geocentric") system of crystalline spheres
dominated astronomy for 2000 years. Aristarchus in 270
B.C. was ahead of his time in suggesting that the sun is at
the center of the universe, and that the earth spins like a
top. Eratosthenes (ca. 200 B.C.) calculated the size
of the earth; Hipparchus (2nd century B.C.) calculated
the distance to the moon and established a system of latitudes
and longitudes. Ptolemy (1st century A.D.) published
the great compilation of astronomical knowledge (the Almagest),
and he offered the epicycle theory to explain new observations
not explained by the geocentric theory of the universe.
In
1543, the Polish astronomer Nicolaus Copernicus overturned
the geocentric theory by publishing a book on his heliocentric
(sun-centered) theory. Johannes Kepler soon joined the
great astronomer Tycho Brahe, systematizing Tycho's observations
with calculations proving that orbits are elliptical. Kepler
also established his three great laws of celestial motion. Galileo
improved the telescope and discovered many new astronomical
features; his work publicly discredited the geocentric doctrine,
leading to the famous recantation forced upon him by the church.
Galileo's celestial and terrestrial discoveries laid the foundation
for the great advances and discoveries of Isaac
Newton.
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